Method and apparatus for programmable fluidic processing

ABSTRACT

A method and apparatus for microfluidic processing by programmably manipulating a packet. A material is introduced onto a reaction surface and compartmentalized to form a packet. A position of the packet is sensed with a position sensor. A programmable manipulation force is applied to the packet at the position. The programmable manipulation force is adjustable according to packet position by a controller. The packet is programmably moved according to the programmable manipulation force along arbitrarily chosen paths.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to fluidic processingand, more particularly, to a method and apparatus for programmablymanipulating and interacting one or more compartmentalized packets ofmaterial on a reaction surface.

[0003] 2. Description of Related Art

[0004] Chemical protocols often involve a number of processing stepsincluding metering, mixing, transporting, division, and othermanipulation of fluids. For example, fluids are often prepared in testtubes, metered out using pipettes, transported into different testtubes, and mixed with other fluids to promote one or more reactions.During such procedures, reagents, intermediates, and/or final reactionproducts may be monitored, measured, or sensed in analytical apparatus.Microfluidic processing generally involves such processing andmonitoring using minute quantities of fluid. Microfluidic processingfinds applications in vast fields of study and industry including, forinstance, diagnostic medicine, environmental testing, agriculture,chemical and biological warfare detection, space medicine, molecularbiology, chemistry, biochemistry, food science, clinical studies, andpharmaceutical pursuits.

[0005] A current approach to fluidic and microfluidic processingutilizes a number of microfluidic channels that are configured withmicrovalves, pumps, connectors, mixers, and detectors. While devicesusing micro-scale implementations of these traditional approaches mayexhibit at least a degree of utility, vast room for improvement remains.For instance, pumps and valves used in traditional fluidictransportation are mechanical. Mechanical devices, particularly whencoupled to thin microchannels, may be prone to failure or blockage. Inparticular, thin channels may become narrowed or partially-blocked dueto buildup of channel contamination, which, in turn, may lead tomechanical failure of associated devices. Current microfluidic devicesalso lack flexibility, for they rely upon a fixed pathway ofmicrochannels. With fixed pathways, devices are limited in the numberand type of tasks they may perform. Also, using fixed pathways makesmany types of metering, transport, and manipulation difficult. Withtraditional devices, it is difficult to partition one type of samplefrom another within a channel.

[0006] Electrical properties of materials have been employed to performa limited number of fluidic processing tasks. For example,dielectrophoresis has been utilized to aid in the characterization andseparation of particles, including biological cells. An example of sucha device is described in U.S. Pat. No. 5,344,535 to Betts, incorporatedherein by reference. Betts establishes dielectrophoretic collectionrates and collection rate spectra for dielectrically polarizableparticles in a suspension. Particle concentrations at a certain locationdownstream of an electrode structure are measured using a light sourceand a light detector, which measures the increased or decreasedabsorption or scattering of the light which, in turn, indicates anincrease or decrease in the concentration of particles suspended in thefluid. Although useful for determining particle dielectrophoreticproperties, such a system is limited in application. In particular, sucha system does not allow for general fluidic processing involving variousinteractions, sometimes performed simultaneously, such as metering,mixing, fusing, transporting, division, and general manipulation ofmultiple reagents and reaction products.

[0007] Another example of using certain electrical properties forspecific types of processing is disclosed in U.S. Pat. No. 5,632,957 toHeller et al., incorporated herein by reference. There, controlledhybridization may be achieved using a matrix or array of electronicallyaddressable microlocations in conjunction with a permeation layer, anattachment region and a reservoir. An activated microlocation attractscharged binding entities towards an electrode. When the binding entitycontacts the attachment layer, which is situated upon the permeationlayer, the functionalized specific binding entity becomes covalentlyattached to the attachment layer. Although useful for specific taskssuch as DNA hybridization, room for improvement remains. In particular,such a system, utilizing attachment sites for certain binding entitiesis designed for particular applications and not for general fluidicprocessing of a variety of fluids. More specifically, such a system isdesigned for use with charged binding entities that interact withattachment sites.

[0008] Another example of processing is disclosed in U.S. Pat. No.5,126,022 to Soane et al., incorporated herein by reference. There,charged molecules may be moved through a medium that fills a trench inresponse to electric fields generated by electrodes. Although useful fortasks such as separation, room for improvement remains in that suchdevices are not well suited for performing a wide variety of fluidicprocessing interactions on a wide variety of different materials.

[0009] There are other examples of using dielectrophoresis forperforming specific, limited fluidic processing tasks. U.S. Pat. No.5,795,457 to Pethig and Burt, incorporated herein by reference, disclosea method for promoting reactions between particles suspended in liquidby applying two or more electrical fields of different frequencies toelectrode arrays. While perhaps useful for facilitating certaininteractions between many particles of different types, the method isnot well suited for general fluidic processing. U.S. Pat. No. 4,390,403to Batchelder, incorporated herein by reference, discloses a method andapparatus for manipulation of chemical species by dielectrophoreticforces. Although useful for inducing certain chemical reactions, itsflexibility is limited, and it does not allow for general, programmablefluidic processing.

[0010] Any problems or shortcomings enumerated in the foregoing are notintended to be exhaustive but rather are among many that tend to impairthe effectiveness of previously known processing techniques. Othernoteworthy problems may also exist; however, those presented aboveshould be sufficient to demonstrated that apparatus and methodsappearing in the art have not been altogether satisfactory.

SUMMARY OF THE INVENTION

[0011] In one respect, the invention is an apparatus for programmablymanipulating a packet. As used herein, “packet” refers tocompartmentalized matter and may refer to a fluid packet, anencapsulated packet, and/or a solid packet. A fluid packet refers to oneor more packets of liquids or gases. A fluid packet may refer to adroplet or bubble of a liquid or gas. A fluid packet may refer to adroplet of water, a droplet of reagent, a droplet of solvent, a dropletof solution, a droplet of sample, a particle or cell suspension, adroplet of an intermediate product, a droplet of a final reactionproduct, or a droplet of any material. An example of a fluid packet is adroplet of aqueous solution suspended in oil. An encapsulated packetrefers to a packet enclosed by a layer of material. An encapsulatedpacket may refer to vesicle or other microcapsule of liquid or gas thatmay contain a reagent, a sample, a particle, a cell, an intermediateproduct, a final reaction product, or any material. The surface of anencapsulated packet may be coated with a reagent, a sample, a particleor cell, an intermediate product, a final reaction product, or anymaterial. An example of an encapsulated packet is a lipid vesiclecontaining an aqueous solution of reagent suspended in water. A solidpacket refers to a solid material that may contain, or be covered with areagent, a sample, a particle or cell, an intermediate product, a finalreaction product, or any material. An example of a solid packet is alatex microsphere with reagent bound to its surface suspended in anaqueous solution. Methods for producing packets as defined herein areknown in the art. Packets may be made to vary greatly in size and shape,but in embodiments described herein, packets may have a diameter betweenabout 100 nm and about 1 cm.

[0012] In this respect, the invention includes a reaction surface, aninlet port, means for generating a programmable manipulation force uponthe packet, a position sensor, and a controller. The reaction surface isconfigured to provide an interaction site for the packet. The inlet portis coupled to the reaction surface and is configured to introduce thepacket onto the reaction surface. The means for generating aprogrammable manipulation force upon the packet programmably moves thepacket about the reaction surface along arbitrarily chosen paths. Asused herein, by “arbitrarily chosen paths” it is meant that paths may bechosen to have any shape about the reaction surface. Arbitrarily chosenpaths are not limited to movements that are predefined. Arbitrarilychosen paths may be modified in an unlimited manner about the reactionsurface and may hence trace out any pattern. The position sensor iscoupled to the reaction surface and is configured to sense a position ofthe packet on the reaction surface. The controller is coupled to themeans for generating a programmable manipulation force and to theposition sensor. The controller is configured to adjust the programmablemanipulation force according to the position.

[0013] In other aspects, the apparatus may also include an outlet portcoupled to the reaction surface. The outlet port may be configured tocollect the packet from the reaction surface. The means for generating amanipulation force may include a conductor adapted to generate anelectric field. The means for generating a manipulation force mayinclude a light source. The manipulation force may include adielectrophoretic force, an electrophoretic force, an optical force, amechanical force, or any combination thereof. The position sensor mayinclude a conductor configured to measure an electrical impedance of thepacket. The position sensor may include an optical system configured tomonitor the position of the packet. The means for generating aprogrammable manipulation force and the position sensor may be integral.

[0014] In another respect, the invention is an apparatus formicrofluidic processing by programmably manipulating packets. Theapparatus includes a reaction surface, an inlet port, an array ofdriving electrodes, and an array of impedance sensing electrodes. Asused herein, an “array” refers to any grouping or arrangement. An arraymay be a linear arrangement of elements. It may also be a twodimensional grouping having columns and rows. Columns and rows need notbe uniformly spaced or orthogonal. An array may also be any threedimensional arrangement. The reaction surface is configured to providean interaction site for the packets. The inlet port is coupled to thereaction surface and is configured to introduce the packets onto thereaction surface. The array of driving electrodes is coupled to thereaction surface and is configured to generate a programmablemanipulation force upon the packets to direct the microfluidicprocessing by moving the packets along arbitrarily chosen paths. Thearray of impedance sensing electrodes is coupled to the reaction surfaceand is configured to sense positions of the packets during themicrofluidic processing.

[0015] In other aspects, the apparatus may also include an outlet portcoupled to the reaction surface. The outlet port may be configured tocollect the packets from the reaction surface. The apparatus may alsoinclude a controller coupled to the array of driving electrodes and tothe array of impedance sensing electrodes. The controller may be adaptedto provide a feedback from the array of impedance sensing electrodes tothe array of driving electrodes. The array of driving electrodes and thearray of impedance sensing electrodes may be integral. The apparatus mayalso include an integrated circuit coupled to the array of drivingelectrodes and to the array of impedance sensing electrodes. Theapparatus may also include a coating modifying a hydrophobicity of thereaction surface. The apparatus may also include a maintenance port.

[0016] In another respect, the invention is an apparatus for processingpackets in a partitioning medium. As used herein, a “partitioningmedium” refers to matter that may be adapted to suspend andcompartmentalize other matter to form packets on a reaction surface. Apartitioning medium may act by utilizing differences in hydrophobicitybetween a fluid and a packet. For instance, hydrocarbon molecules mayserve as a partitioning medium for packets of aqueous solution becausemolecules of an aqueous solution introduced into a suspendinghydrocarbon fluid will strongly tend to stay associated with oneanother. This phenomenon is referred to as a hydrophobic effect, and itallows for compartmentalization and easy transport of packets upon orover a surface. A partitioning medium may also be a dielectric carrierliquid which is immiscible with sample solutions. Other suitablepartitioning mediums include, but are not limited to, air, aqueoussolutions, organic solvents, oils, and hydrocarbons. The apparatusincludes a chamber, a programmable dielectrophoretic array, and animpedance sensing array. As used herein, a “programmabledielectrophoretic array” (PDA) refers to an electrode array whoseindividual elements can be addressed with different electrical signals.The addressing of electrode elements with electrical signals mayinitiate different field distributions and generate dielectrophoreticmanipulation forces that trap, repel, transport, or perform othermanipulations upon packets on and above the electrode plane. Byprogrammably addressing electrode elements within the array withelectrical signals, electric field distributions and manipulation forcesacting upon packets may be programmable so that packets may bemanipulated along arbitrarily chosen or predetermined paths. The chamberis configured to contain the packets and the partitioning medium. Theprogrammable dielectrophoretic array is coupled to the chamber and isconfigured to generate a programmable dielectrophoretic force to directprocessing of the packets. The impedance sensing array of electrodes isintegral with the programmable dielectrophoretic array. The impedancesensing array of electrodes is configured to sense a position of thepackets within the chamber.

[0017] In other aspects, the apparatus may also include an integratedcircuit coupled to the programmable dielectrophoretic array and to theimpedance sensing array of electrodes. The apparatus may also include acontroller coupled to the programmable dielectrophoretic array and tothe impedance sensing array of electrodes. The controller may be adaptedto provide a feedback from the impedance sensing array of electrodes tothe programmable dielectrophoretic array. The electrodes may be betweenabout 1 micron and about 200 microns and may be spaced between about 1micron and about 200 microns.

[0018] In another respect, the invention is a method for manipulating apacket in which the following are provided: a reaction surface, an inletport coupled to the reaction surface, means for generating aprogrammable manipulation force upon the packet, a position sensorcoupled to the reaction surface, and a controller coupled to the meansfor generating a programmable manipulation force and to the positionsensor. A material is introduced onto the reaction surface with theinlet port. The material is compartmentalized to form the packet. Aposition of the packet is sensed with the position sensor. Aprogrammable manipulation force is applied on the packet at the positionwith the means for generating a programmable manipulation force. Theprogrammable manipulation force is adjustable according to the positionby the controller. The packet is programmably moved according to theprogrammable manipulation force along arbitrarily chosen paths.

[0019] In other aspects, the packet may include a fluid packet, anencapsulated packet, or a solid packet. The compartmentalizing mayinclude suspending the material in a partitioning medium. The materialmay be immiscible in the partitioning medium. The reaction surface mayinclude a coating, and the hydrophobicity of the coating may be greaterthan a hydrophobicity of the partitioning medium. The application of theprogrammable manipulation force may include applying a driving signal toone or more driving electrodes arranged in an array to generate theprogrammable manipulation force. The programmable manipulation force mayinclude a dielectrophoretic force, an electrophoretic force, an opticalforce, a mechanical force, or any combination thereof. The sensing of aposition may include applying a sensing signal to one or more impedancesensing electrodes arranged in an array to detect an impedanceassociated with the packet.

[0020] In another respect, the invention is a method of fluidicprocessing in which the following are provided: a reaction surface, aninlet port coupled to the reaction surface, an array of drivingelectrodes coupled to the reaction surface, and an array of impedancesensing electrodes coupled to the reaction surface. One or morematerials are introduced onto the reaction surface with the inlet port.The one or more materials are compartmentalized to form a plurality ofpackets. A sensing signal is applied to one or more of the impedancesensing electrodes to determine a position of one or more of theplurality of packets. A driving signal is applied to one or more of thedriving electrodes to generate a programmable manipulation force on oneor more of the plurality of packets at the position. One or more of theplurality of packets are interacted according to the programmablemanipulation force.

[0021] In other aspects, at least one of the plurality of packets mayinclude a fluid packet, an encapsulated packet, or a solid packet. Thesensing signal and the driving signal may be a single processing signal.The processing signal may include a first frequency componentcorresponding to the sensing signal and a second frequency componentcorresponding to the driving signal. A packet distribution map may beformed according to the positions of the plurality of packets. Aposition of one or more obstructions on the reaction surface may bedetermined. The interacting of one or more packets may include moving,fusing, merging, mixing, reacting, metering, dividing, splitting,sensing, collecting, or any combination thereof.

[0022] In another respect, the invention is a method for manipulatingone or more packets on a reaction surface in which the following areprovided: a programmable dielectrophoretic array coupled to the reactionsurface and an impedance sensing array of electrodes integral with theprogrammable dielectrophoretic array. A material is introduced onto thereaction surface. The material is compartmentalized to form the one ormore packets. A path is specified upon the reaction surface. Aprogrammable manipulation force is applied with the programmabledielectrophoretic array on the one or more packets to move the one ormore packets along the path. A position of the one or more packets issensed with the impedance sensing array of electrodes. Whether theposition corresponds to the path is monitored. The one or more packetsare interacted.

[0023] In other aspects, at lease one of the one or more packets mayinclude a fluid packet, an encapsulated packet, or a solid packet. Themethod may also include sensing a position of an obstruction;determining a modified path, the modified path avoiding the obstruction;and applying a programmable manipulation force on the one or morepackets to move the one or more packets along the modified path. Thespecification of a path may include specifying an initial position and afinal position. The introduction of the material may include extractingthe material with a dielectrophoretic extraction force from an injectoronto the reaction surface. The interacting of one or more packets mayinclude moving, fusing, merging, mixing, reacting, metering, dividing,splitting, sensing, collecting, or any combination thereof.

[0024] Other features and advantages of the present invention willbecome apparent with reference to the following description of typicalembodiments in connection with the accompanying drawings wherein likereference numerals have been applied to like elements, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a simplified schematic diagram that illustrates amicrofluidic device according to one embodiment of the presentlydisclosed method and apparatus.

[0026]FIG. 2 is a simplified illustration of dielectrophoretic forcephenomenon.

[0027]FIG. 3 illustrates a position sensing system according to oneembodiment of the presently disclosed method and apparatus.

[0028]FIG. 4 is a three dimensional view of a microfluidic deviceaccording to one embodiment of the presently disclosed method andapparatus.

[0029]FIG. 5 is a side cross sectional view of a microfluidic deviceaccording to one embodiment of the presently disclosed method andapparatus.

[0030]FIG. 6 is a simplified block representation of a microfluidicsystem according to one embodiment of the presently disclosed method andapparatus.

[0031]FIG. 7 is a simplified block representation of a signalapplication arrangement according to one embodiment of the presentlydisclosed method and apparatus.

[0032]FIG. 8 is a cross sectional view of microfluidic device accordingto one embodiment of the presently disclosed method and apparatus.

[0033]FIG. 9 is a top view of a microfluidic device according to oneembodiment of the presently disclosed method and apparatus.

[0034]FIG. 9B is another top view of a microfluidic device according toone embodiment of the presently disclosed method and apparatus.

[0035]FIG. 10 is a simplified block representation of a microfluidicsystem according to one embodiment of the presently disclosed method andapparatus.

[0036]FIG. 11 is a top view of a microfluidic device showing amicrofluidic process according to one embodiment of the presentlydisclosed method and apparatus.

[0037]FIG. 12 illustrates certain packet interactions according to oneembodiment of the presently disclosed method and apparatus.

[0038]FIG. 13 is a flow chart showing a microfluidic process accordingto one embodiment of the presently disclosed method and apparatus.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0039] The disclosed method and apparatus provide many advantages. Forinstance, they permit the fluidic processing of minute quantities ofsamples and reagents. The apparatus need not use conventional hardwarecomponents such as valves, mixers, pump. The apparatus may be readilyminiaturized and its processes may be automated or programmed. Theapparatus may be used for many different types of microfluidicprocessing and protocols, and it may be operated in parallel modewhereby multiple fluidic processing tasks and reactions are performedsimultaneously within a single chamber. Because it need not rely onnarrow tubes or channels, blockages may be minimized or eliminated.Further, if obstructions do exist, those obstructions may be located andavoided with position sensing techniques.

[0040] Allowing for flexible microfluidic processing, the disclosedmethod and apparatus has vast applications including, but not limitedto, blood and urine assays, pathogen detection, pollution monitoring,water monitoring, fertilizer analysis, the detection of chemical andbiological warfare agents, food pathogen detection, quality control andblending, massively parallel molecular biological protocols, geneticengineering, oncogene detection, and pharmaceutical development andtesting.

[0041] In one embodiment of the disclosed method and apparatus, afluidic device 10 as shown in FIG. 1 is employed. As illustrated,fluidic device 10 may include a reaction surface 12, a port 15, packets21, wall 22, position sensor 23, a force generator 25, and a controller81.

[0042] In operation, one or more materials may be introduced ontoreaction surface 12 through port 15. The one or more materials may becompartmentalized to form packets 21 within a partitioning medium (notshown). Force generator 25 generates a manipulation force on packets 21to facilitate fluidic manipulations and interactions. In the illustratedembodiment, force generator 25 generates two forces, F₁ and F₂, thatmanipulate packets 21 and moves them according to the dashed lines ofFIG. 1. Position sensor 23 senses the positions of packets 21 and isable to monitor any packet interactions. As position sensor 23 iscoupled to force generator 25 by controller 81, a feedback relationshipmay be established. Such feedback may include determination of theposition of packets 21 on reaction surface 12 that allows for theapplication of manipulation forces on packets 21 based on positioninformation. The position of packets during manipulation may thus becontinuously monitored and this information may be used to continuouslyadjust one or more manipulation forces so to achieve movement of packets21 along a desired trajectory to a desired location on reaction surface12.

[0043] In the illustrated embodiment of FIG. 1, forces F₁ or F₂ mayinclude many different types of forces. For instance, forces F₁ and F₂may be dielectrophoretic, electrophoretic, optical (as may arise, forexample, through the use of optical tweezers), mechanical (as may arise,for example, from elastic traveling waves or from acoustic waves), orany other suitable type of force (or combination thereof). In oneembodiment, forces F₁ and F₂ may be programmable. Using programmableforces, packets may be manipulated along arbitrarily chosen paths.

[0044] In the illustrated embodiment of FIG. 1, position sensor 23 maybe operated with various mechanisms to sense positions of packets 21.For instance, an optical imaging system may be used to determine andmonitor packet positions. Specifically, an optical microscope may beconnected to a CCD imaging camera, which may be interfaced with animaging card in a computer. The information from the imaging card may beprocessed in the computer using image-analysis software. Alternatively,a CCD imaging device may be incorporated in or above the reactionsurface 12 to monitor the positions of packets. Thus, positions ofpackets and their movement on reaction surface 12 may be continuouslymonitored and recorded in the computer. A different mechanism of packetposition sensing uses electrical impedance measurements. The presence orabsence of a packet between two electrode elements may affect theelectrical impedance between the electrodes. Thus, measurement ofelectrical impedance between electrode elements may allow for indirectmonitoring of packet positions.

[0045] In order to better understand the operation and design of thecurrently disclosed method and apparatus, which will be discussed firstin relation to dielectrophoretic forces, it is useful to discussdielectrophoretic theory in some detail. Such a discussion is aided byFIG. 2, which illustrates two packets, 21 a and 21 b, both beingsubjected to dielectrophoretic forces.

[0046] Dielectrophoretic forces may arise when a packet is placed in aninhomogeneous electrical field (AC or DC). In FIG. 2 the electricalfield is weaker on the left side than on the right side. An electricalfield induces electrical polarizations in the packet. The polarizationcharges are depicted at the two ends of the packets 21 a and 21 b alongthe field lines 35. Dielectrophoretic forces result from the interactionbetween the induced polarization (labeled as m₁ and m₂ in FIG. 2) andthe applied inhomogeneous field. If a packet is suspended in a mediumhaving different dielectric properties, such as a partitioning medium,then the packet may remain compartmentalized and may readily respond tomanipulation forces against viscous drag. In a field of non-uniformstrength, a packet may be directed towards either strong (packet 21 a)or weak (packet 21 b) electrical field regions, depending on whether thepacket is more (packet 21 a) or less (packet 21 b) polarizable than apartitioning medium. In a field of non-uniform phase distribution (i.e.a traveling electrical field), a packet may be directed towards fieldregions of larger or smaller phase distribution, depending whether thepacket has a longer or shorter dielectric response time than that of apartitioning medium.

[0047] DEP Theory

[0048] When a packet of radius r, suspended in an immiscible medium ofdifferent dielectric properties, is subjected to an electrical field offrequency f, the polarization of the packet can be represented using aneffective dipole moment (Wang et al., “A Unified Theory ofDielectrophoresis and Traveling Wave Dielectrophoresis”, Journal ofPhysics D: Applied Physics, Vol 27, pp. 1571-1574, 1994, incorporatedherein by reference)

{right arrow over (m)}(f)=4πε_(m) r ³ P _(CM)(f){right arrow over(E)}(f)  (1)

[0049] where {right arrow over (m)}(f) and {right arrow over (E)}(f) arethe dipole moment and field vectors in the frequency domain, P_(CM)(f)is the so-called Clausius-Mossotti factor, given by

P _(CM)(f)=(ε_(d) ^(*)−ε_(m) ^(*))/(ε_(d) ^(*)+2ε_(m) ^(*)).  (2)

[0050] Here ε_(k) ^(*)=ε_(k)−jσ_(k)/(2πf) are the complex permittivitiesof the packet material (k=d) and its suspension medium (k=m), and ε andσ refer to the dielectric permittivity and electrical conductivity,respectively. Using the effective dipole moment method, the DEP forcesacting on the packet are given by

{overscore (F)}(f)=2πr ³ε_(m)(Re[P(f)]∇E _(rms) ² +Im[P(f)](E _(x0)²∇φ_(x0) +E _(y0) ²∇φ_(y0) +E _(z0) ²∇φ_(z0)))  (3)

[0051] where E(rms) is the RMS value of the field strength, E_(i0) andφ_(i0) (i=x; y;z) are the magnitude and phase, respectively, of thefield components in a Cartesian coordinate frame. Equation (3) showsthat the DEP force contains two independent terms. The first, relatingto the real (in phase) part of the polarization factor Re[P(f)] and tonon-uniformities in the field magnitude (∇E_((rms)) ²). Depending on thesign of Re[P(f)], this force directs the packet either toward strong orweak field regions. The second term relates to the imaginary (out ofphase) part of the polarization factor (Im[P(f)]) and to field phasenon-uniformities (∇φ_(i0), i=x; y; z) that correspond to the fieldtraveling through space from large to small phase regions. Depending onthe sign of Im[P(f)], this directs packets toward regions where thephase values of the field components are larger or smaller.

[0052] Equations (1-3) indicate that the DEP phenomena have thefollowing characteristics:

[0053] (1) DEP forces experienced by packets are dependent on thedielectric properties of the packets (ε_(d) ^(*)) and the partitioningmedium (ε_(m) ^(*)).

[0054] (2) The strong dependence of three-dimensional DEP forces on thefield configuration allows for versatility in implementingdielectrophoretic manipulations.

[0055] DEP Forces on Packets

[0056] In one embodiment, a conventional dielectrophoresis component maybe used for packet manipulation. In this case, the DEP force is given by

{overscore (F)}(f)=2πr ³ε_(m) Re[P(f)]∇E _((rms)) ²  (4)

[0057] where r is the packet radius, ε_(m) is the dielectricpermittivity of the suspending fluid. Re[P(f)] is the real (in phase)part of the polarization factor and ∇E_((rms)) ² is the fieldnon-uniformity factor. For packets of water (ε=78 and σ>10⁻⁴ S/m)suspended in a hydrocarbon fluid (ε=˜2 and σ˜0), the factor Re[P(f)] isalways positive and close to unity. Therefore, water packets are alwaysattracted towards regions of large field strength. For example, if anelectrode array composed of circular electrodes arranged in a hexagonalfashion is provided, water packets may be dielectrophoretically movedtowards and trapped between, for example, an electrode pair, over asingle electrode, or above a plurality of electrodes to which electricalsignals are applied. Switching the electrical signals may result inmovement of the DEP traps and may cause water packets to move in achamber. Thus, packet manipulation may be realized by switchingelectrical signals applied to an electrode array so that DEP field trapsare made “mobile” within a chamber.

[0058] Typical Forces and Velocities

[0059] For a water packet of 100 μm suspended in a hydrocarbon fluidsuch as decane, the DEP force may be on the order of 1000 pN if thefield non-uniformity is 1.25×10¹³ V²/m³ (equivalent to 5V RMS applied toan electrode pair of distance 50 μm with the field decaying to zero at1000 μm). If the viscosity of the hydrocarbon fluid is small (0.838 mPafor Decane), the packet velocity may be of the order of 600 μm/sec,indicating that fast manipulation of packets is possible with electrodearrays. In the above analysis, DEP force equation (4) has been used,which was developed for non-deformable particles and holds well forsuspended particles (such as cells, latex particles). Fluid packets maybe deformed under the influence of applied electrical field, affectingthe accuracy of equation (4) in describing DEP forces for packets.Nevertheless, equation (4) should be generally applicable with somepossible correction factors for different packet shapes.

[0060]FIG. 3 shows one possible implementation of position sensor 23 ofFIG. 2. Shown in FIG. 3 are five impedance sensing electrodes 19, hereillustrated as 19 a, 19 b, 19 c, 19 d, and 19 e. Each sensing electrode19 may be coupled to an impedance sensor 29, here illustrated asimpedance sensors 29 a, 29 b, 29 c, and 29 d. In one embodiment,impedance sensing electrodes 19 may be positioned in operativerelationship with surface 12 of fluidic device 10 in FIG. 1. Forinstance, sensing electrodes 19 may be placed on or near surface 12. Aspackets 21 are manipulated about surface 12 by the application ofappropriate manipulation forces, impedance sensing electrodes 19 andsensors 29 may sense a position of packets 21 by making one or moreimpedance measurements.

[0061] If the dielectric medium above an electrode is displaced by apacket having different dielectric and/or conductive properties, theimpedance detected at the electrode element will change. Thus, one maydetermine the position of packets 21 by noting the impedancemeasurements associated therewith. As is shown in FIG. 3, the impedancebetween impedance sensing electrodes 19 a and 19 b is “high” (seeimpedance sensor 29 d) relative to, for instance, the impedance betweenimpedance sensing electrodes 19 b and 19 c (see impedance sensor 29 c).Thus, by pre-determining that the “high” impedance value corresponds tothe impedance due to the partitioning medium, it may be deduced thatsome material of different impedance to the partitioning medium liessomewhere between impedance sensing electrodes 19 d and 19 e and between19 b and 19 c because the impedance associated with those electrodes is“low” (see impedance sensor 29 a). By like reasoning, one may assumethat no packet lies between impedance sensing electrodes 19 c and 19 d,for the impedance between those two electrodes is relatively “high” (seeimpedance sensor 29 b and 29 c).

[0062] Those of skill in the art will appreciate that the “low” and“high” values discussed above may be reversed, depending upon therelative impedances of a packet and of a suspending medium. In otherwords, in some situations, a relatively “high” impedance measurement maysignal the presence of a packet in between a pair of electrodes while arelatively “low” impedance may signal the lack of a packet. Those ofskill in the art will also appreciate that individual impedancemeasurements may exhibit a wide range of values (not just “low” or“high”), and it may be possible to characterize different types andsizes of materials by noting their associated impedance measurements.For instance, one may be able to differentiate, by type, the two packets21 of FIG. 3 by noting any differences in their impedance readings onimpedance sensors 29 a and 29 c.

[0063] Impedance sensing may be based on the so-called mixture theory,which associates the impedance of a heterogeneous system with thedielectric properties of various system components and their volumefractions. Take a two-component, heterogeneous system where component 2having complex dielectric permittivity$\left( {{ɛ_{2}^{*} = {ɛ_{2} - {j\quad \frac{\sigma_{2}}{2\pi \quad f}}}},{f\quad {is}\quad {the}\quad {frequency}}} \right)$

[0064] and a volume fraction α is suspended in component 1 havingcomplex dielectric permittivity$\left( {ɛ_{1}^{*} = {ɛ_{1} - {j\quad \frac{\sigma_{1}}{2\pi \quad f}}}} \right).$

[0065] ). The complex permittivity of the total system is given by (Wanget al., “Theoretical and experimental investigations of theinterdependence of the dielectric, dielectrophoretic andelectrorotational behavior of colloidal particles” in J. Phys. D: Appl.Phys. 26: 312-322, 1993, incorporated herein by reference)$ɛ_{sys}^{*} = {ɛ_{1}^{*}{\frac{\frac{1}{\alpha} + {2\frac{ɛ_{2}^{*} - ɛ_{1}^{*}}{ɛ_{2}^{*} + {2ɛ_{1}^{*}}}}}{\frac{1}{\alpha} + \frac{ɛ_{2}^{*} - ɛ_{1}^{*}}{ɛ_{2}^{*} + {2ɛ_{1}^{*}}}}.}}$

[0066] The total impedance of the system, which is assumed to havelength L and cross-sectional area A, is given by$\Omega = {\frac{L}{{\omega ɛ}_{sys}^{*}A}.}$

[0067] The electrical impedance between two electrode elements in thepresence or absence of a packet may be analyzed using the aboveequations, with the parameters L and A determined experimentally. Theexistence of a packet may correspond to α>0 and the absence of a packetmay correspond to α=0. From these equations, an impedance change wouldoccur when a packet having different dielectric property (ε₂ ^(*)) fromthe partitioning media (ε₁ ^(*)) is introduced into the space betweenthe two electrode elements.

[0068] A relatively low impedance measurement may indicate anobstruction or a packet (as is illustrated in FIG. 3) on or near surface12. By determining impedance values, one may map locations ofobstructions or packets relative to surface 12. In this way, one maygenerate a packet and/or obstruction distribution map with respect toreaction surface 12 of fluidic device 10. With the benefit of thisdisclosure, one of skill in the art will appreciate that the descriptionassociated with FIG. 3 may be implemented in many different ways. Inparticular, one may use any suitable type of impedance measurementdevices known in the art to function with one or more electrodes. Suchdevices may include an impedance analyzer, a DC/AC conductance meter, orany circuit based upon methods of operation of these or otherinstruments having similar function.

[0069]FIG. 4 shows a three dimensional view of one embodiment of afluidic device 10 according to the present disclosure. Fluidic device 10includes reaction surface 12, an inlet port 14, an outlet port 16,driving electrodes 18, impedance sensing electrodes 19, connectors 20,and wall 22.

[0070] Reaction surface 12 provides an interaction site for packets. Inone embodiment, reaction surface 12 may be completely or partiallycovered with a partitioning medium (not shown in FIG. 4) or othersubstance. In one embodiment, reaction surface 12 may be coated. Inparticular, for manipulation of aqueous packets in a hydrophobicpartitioning medium, reaction surface 12 may include a hydrophobiccoating, or layer, having a hydrophobicity similar to or greater thanthe hydrophobicity of the partitioning medium. Such a coating mayprevent an aqueous packet from sticking, from spreading, or frombecoming unstable upon contact with reaction surface 12. Additionally, acoating may modify association and/or interaction forces between packetsand reaction surfaces to facilitate manipulation of packets byappropriate manipulation forces. Further, a coating may be used toreduce contamination of reaction surfaces by reagents in packets. Stillfurther, a coating may facilitate the deliberate adhesion, wetting, orsensing of packets at or on reaction surfaces. If a dielectric layercoating is applied, the layer should be made sufficiently thin to allowAC electric field penetration through the dielectric layer. In oneembodiment, the thickness of the layer may be between about 2 nm andabout 1 micron. In one embodiment, a hydrophobic coating may be Teflonthat may be applied by means known in the art such as sputtering orspin-coating. It is to be understood that any other suitable coatingthat modifies an interaction between packets and the reaction surfacemay be used.

[0071] Reaction surface 12 may be formed from a number of suitablematerials. In the illustrated embodiment, reaction surface 12 is aplanar surface that has an upper surface including driving electrodes 18and impedance sensing electrodes 19. Although illustrated as beingcoplanar with reaction surface 12, it is to be understood that drivingelectrodes 18 and 19 may also be elevated or depressed with respect toreaction surface 12. Likewise, reaction surface 12 need not be planar.Rather, it may have concave or convex portions, or it may be deformed insome other manner. Reaction surface 12 may be glass, silicon dioxide, apolymer, a ceramic, or any suitable electrically insulating material.The dimensions of reaction surface 12 may vary widely depending on theapplication but may be between about 20 microns by about 20 microns andabout 50 centimeters by about 50 centimeters. More particularly,reaction surface 12 may be between about 3 millimeters by about 3millimeters and about 30 centimeters by about 30 centimeters.

[0072] Inlet port 14 may be adapted to inject or introduce materialsonto reaction surface 12 and may be any structure allowing ingress toreaction surface 12. In the illustrated embodiment, inlet port 14consists of an opening in wall 22. Such an opening may be of anysuitable size or shape. Alternatively, inlet port 14 may be a syringeneedle a micropipette, a tube, an inkjet injector, or any other suitabledevice able to inject a material for introduction onto reaction surface12. Using a micropipette or equivalent device, wall 22 may not need toinclude any openings. Rather, material may be introduced onto reactionsurface 12 from above. A micropipette or any other equivalent device maybe attached to a micromanipulation stage (not shown in FIG. 4) so thatmaterial may be precisely deposited onto specific locations of reactionsurface 12. In one embodiment, inlet port 14 may consist of acylindrical tube opening onto reaction surface 12. Such a tube may havea diameter of between about 1 micrometer and about 1 mm and, moreparticularly, between about 10 and 100 microns.

[0073] Outlet port 16 may be adapted to collect packets of material fromreaction surface 12. Outlet port 16 may be any structure allowing egressfrom reaction surface 12. In the illustrated embodiment, outlet port 16consists of an opening in wall 22. The opening may be of any suitablesize or shape. Alternatively, outlet port 16 may be a micropipette orany other equivalent device able to collect a material from reactionsurface 12. Wall 22 may not need to include any openings. Rather,packets of material may be collected from reaction surface 12 fromabove. A syringe or any other equivalent device may be attached to amicromanipulation stage (not shown in FIG. 4) so that packets may beprecisely collected from specific locations on reaction surface 12. Inone embodiment, outlet port 16 may consist of a cylindrical tube openingonto reaction surface 12. Such a tube may have a diameter of about 1millimeter and a length of about 3 centimeters or longer.

[0074] In one embodiment, inlet port 14 and outlet port 16 may beintegral. For instance, in the embodiment shown in FIG. 1 port 15 is acylindrical tube opening onto reaction surface 12. In alternativeembodiments, one micropipette may serve as both an inlet port and anoutlet port. Alternatively, a single opening in wall 22 may serve bothinput and output functions. In another embodiment, multiple inlet andoutlet ports may be utilized.

[0075] Fluidic device 10 may include an arbitrary number of inlet andoutlet ports. For example, any one of the three unnumbered openings inwall 22, illustrated in FIG. 4, may serve as an inlet port, an outletport, or an integral inlet-outlet port, such as port 15 of FIG. 1. Inanother embodiment, multiple inlet and/or outlet ports may extendcompletely or partially along a wall 22 so that materials may beintroduced and/or collected to and/or from reaction surface 12. In suchan embodiment, one may more precisely introduce or collect materials.

[0076] In FIG. 4, driving electrode 18 is one of a number of otherdriving electrodes arranged in an array upon reaction surface 12. Inthis embodiment, driving electrodes 18 may be associated with forcegenerator 25 of FIG. 1, for the driving electrodes 18 may contribute tothe generation of forces, such as forces F₁ and F₂ of FIG. 1, tomanipulate packets of material on reaction surface 12 to promote, forinstance, microfluidic interactions.

[0077] Dielectrophoretic forces may be generated by an array ofindividual driving electrodes 18 fabricated on an upper surface of areaction surface 12. The driving electrode elements 18 may beindividually addressable with AC or DC electrical signals. Applying anappropriate signal to driving electrode 18 sets up an electrical fieldthat generates a dielectrophoretic force that acts upon a packet, knownto be at a certain location through impedance measurements as describedabove in relation to FIG. 3. Switching different signals to differentelectrodes sets up electrical field distributions within fluidic device10. Such electrical field distributions may be utilized to manipulatepackets in a partitioning medium.

[0078] In particular, the movement of packets under the influence of amanipulation force may be controlled by switching appropriate electricalsignals to different combinations of driving electrodes 18.Specifically, the switching of electrical signals may initiate differentfield distributions and generate manipulation forces that trap, repel,transport, or perform other manipulations upon packets of material. Byprogrammably switching electrical signals to different combinations ofdriving electrodes 18 within an array, electric field distributions andmanipulation forces acting upon packets may be programmable so thatpackets may be manipulated along arbitrarily chosen or predeterminedpaths in a partitioning medium along reaction surface 12. Thus, packetsmay be manipulated in an unlimited manner. Signals may be appropriatelyswitched to cause, for instance, a packet to move a single “unitdistance”—a distance between two neighboring electrodes. Further, byprogrammably switching electrical signals, different microfluidicreactions may be performed in series or in parallel. An electrode arrayhaving such an ability to utilize programmable dielectrophoretic forcesby programmed switching of electrical signals to different combinationsof driving electrodes 18 may be termed a programmable dielectrophoreticarray (PDA).

[0079] In FIG. 4, impedance sensing electrode 19 is one of a number ofother impedance sensing electrodes arranged in an array upon reactionsurface 12. In this embodiment, impedance sensing electrodes 19 may beassociated with position sensor 23 of FIG. 1 and is illustrated in FIG.3. Impedance sensing electrodes 19 contribute to the sensing of packetpositions upon reaction surface 12 so that those packets of material maybe monitored and manipulated according to position.

[0080] In the illustrated embodiment, driving electrodes 18 andimpedance sensing electrodes 19 are electrodes of a two dimensionalelectrode array coupled to a top surface of reaction surface 12. Thesize of the array may vary according to need, but in one embodiment a 16by 16 array is employed. Because fluidic device 10 is scaleable, smalleror larger arrays may be fabricated without significant departure fromthe present disclosure. For example, 256 by 256 arrays or larger may bemade according to the present disclosure. Driving electrodes 18 andimpedance sensing electrodes 19 within an array may be uniformly ornon-uniformly spaced. The spacing may vary widely, but in oneembodiment, the spacing may be between about 2 microns and about 200microns. The electrodes may have different forms such as lines, squares,circles, diamonds, polygons, or other suitable shapes. The dimensions ofeach electrode may vary, but a typical electrode may be between about0.2 microns and about 10 mm., and more particularly, between about 1micron and about 200 microns. Driving electrodes 18 and impedancesensing electrodes 19 may be formed using any method known in the art.In one embodiment, such electrodes may be formed using standardphotolithography techniques. For example, one may refer to, e.g., D. Qinet al, “Microfabrication, Microstructures and Microsystems”, MicrosystemTechnology in Chemistry and Life Sciences (Ed. Manz and Becker),Springer, Berlin, 1997, pp 1-20, which is incorporated herein byreference. Also, one may refer to Madou, Fundamentals ofMicrofabrication, CRC Press, Boca Raton, 1997, which is incorporatedherein by reference. Depending upon the particular application, and thenature of the packets and partitioning medium, the size and spacing ofelectrodes 18 and 19 may be smaller than, of similar size, or largerthan the diameters of the packets.

[0081] In one embodiment, impedance sensing electrodes 19 may beintegral with driving electrodes 18. In such an embodiment, theresulting array may be termed an integral array. With an integral array,a single conductor coupled to reaction surface 12 may serve bothpurposes—driving packets and sensing positions of packets. Thus, aprogrammable manipulation force may be generated upon packets uponreaction surface 12 and a position of those packets may be sensed with asingle electrode array.

[0082] In the embodiment of FIG. 4, wall 22 is adapted to enclose one ormore sides of reaction surface 12. It is to be understood that wall 22may be any suitable structure capable of enclosing one or more sidesand/or the top of reaction surface 12. As illustrated, wall 22 enclosesfour sides of reaction surface 12, defining an open reaction surfacechamber. In a most typical embodiment, the chamber may have a thicknessof between about 10 microns and about 20 millimeters. In anotherembodiment, wall 22 may enclose the top of reaction surface 12, forminga closed reaction chamber.

[0083] Wall 22 may be formed from any suitable material. In oneembodiment, wall 22 may be made from machined plastic, aluminum, glass,plastic, ceramic, or any combination thereof. In one embodiment, wall 22may be partially or completely transparent to certain wavelengths ofradiation. Thus, radiation may be transmitted through wall 22 toinitiate or maintain certain microfluidic reactions or processes forsensing. For instance, a photochemical reaction may be initiated throughwall 22.

[0084] Connectors 20 of FIG. 4 may be adapted to provide electricalconnections to driving electrodes 18 and to impedance sensing electrodes19. Connectors 20 may provide electrical connections to an entire arrayof electrodes, or to preselected ones or groups. In one embodiment,connectors 20 are coupled to a controller (not shown in FIG. 4) that mayadjust a programmable manipulation force distribution generated bydriving electrodes 18 according one or more packets position sensed withimpedance sensing electrodes 19. Thus, such a controller may effectivelyprovide a feedback mechanism between the driving electrodes 18 and theimpedance sensing electrodes 19—The signals applied to drivingelectrodes 18 may be adjusted in view of one or more results from theimpedance sensing electrodes 19.

[0085] Turning now to FIG. 5, there is shown a side cross section viewof a fluidic device 10 according to the present disclosure. Fluidicdevice 10 includes a reaction chamber 41 and an array of integralimpedance sensing and driving electrodes, integral array 43. In theillustrated embodiment, a control chip 60 is coupled to integral array43. Positioned upon a top surface of control chip 60 may be capillarywall 62 that forms a lower surface of a capillary 64. Capillary 64 maylead to an inlet port 14 that leads into chamber 41. Althoughillustrated with only one inlet port, it is contemplated that there maybe several such ports providing access to chamber 41. Above capillary 64is a substrate 66 that, in one embodiment, is made of glass although anysuitable material known in the art may be utilized instead.

[0086] In one embodiment, control chip 60 may be an integrated circuitconfigured to control integrated array 43. Alternatively, control chip60 may be a control interface leading to another controlling device suchas an integrated circuit, computer, or similar device that may controlintegral array 43. Control chip 60 may utilize flip-chip technology orany other suitable technique to establish electrical control overintegral array 43 by switching different signals to and from it.

[0087]FIG. 6 shows a controller 81 according to one embodiment of thepresently disclosed method and apparatus. Controller 81 may include acomputer 80, a signal generator 82, an electrode selector 84, atransducer 88, and a fluidic device 10 having a driving electrode 18 andan impedance sensing electrode 19.

[0088] Computer 80 may be configured to control fluidic device 10 andthe fluid processing occurring upon reaction surface 12. Computer 80 mayhave a user interface that allows for simple programming of signalgenerator 82 and transducer 88, which measures impedance, to allow forprogrammable microfluidic processing. In particular, computer 80 mayprogrammably control the initiation/termination of one or more signalsfrom signal generator 82, the parameters of the one or more signalsincluding frequencies, voltages, and particular waveforms, and controlthe switching of one or more signals from generator 82 to differentcombinations of electrodes 18 and 19.

[0089] Computer 80 may vary signals in many ways. For instance, onesignal having a first frequency component may be sent through electrodeselector 84 to a driving electrode 18 while another signal having asecond, different frequency component may be sent to, for instance, animpedance sensing electrode 19 and through electrode selector 84. Anysequence of signals or combinations of signals may be sent differentcombinations of electrodes and from the fluidic device 10. Any signalparameter may be varied and any electrode selection may be controlled sothat appropriate electric fields may be established at particularlocations upon reaction surface 12. Alternating Current or DirectCurrent signals may be utilized.

[0090] Signal generator 82 may send a driving signal to one or moredriving electrodes 18 while sending a sensing signal to one or moreimpedance sensing electrodes 19. In one embodiment, the driving signaland the sensing signal may comprise a single, composite processingsignal having different frequency components. Such a signal may be usedwith an integrated array to provide (via a single processing signal) afrequency component to generate a programmable manipulation force and afrequency component to provide an impedance sensing signal. Themanipulation and impedance sensing components may also be combined bymultiplexing or switching in time as is known in the art.

[0091] In one embodiment, signal generator 82 provides one or moreprogrammable driving signals to one or more driving electrodes 18through electrode selector 84 so that a programmable alternating-currentelectric field, such as a non-uniform field, may be produced at reactionsurface 12. That electric field may induce polarization of packets ofmaterials adjacent to or in the vicinity of the one or more drivingelectrodes 18. A programmable dielectrophoretic force distribution may,in this manner, be generated that manipulates packets in a controllable,programmable manner so that varied programmable fluidic interactions maytake place upon reaction surface 12.

[0092] In one embodiment, signal generator 82 provides a sensing signalto one or more impedance sensing electrodes 19 so that an impedancemeasurement may be made. The impedance sensing signal may be applied toone or more pairs of impedance sensing electrodes 19 and a change involtage or current may be detected and transmitted to computer 80 viasensing electrodes 88 and wire 86. Computer 80 may then compute theimpedance and hence, determine whether a packet or obstruction waspresent at or near the pair(s) of impedance sensing electrodes 19 beingprobed.

[0093] In an embodiment utilizing a single integrated array (instead ofseparate impedance sensing and driving electrode arrays, an integratedarray utilizes electrodes that function to both drive and sensepackets), the integrated array may both generate a programmablemanipulation force and sense an impedance. In one approach, electricalsensing signals for sensing electrode impedance may be applied atdifferent frequencies from driving signals for manipulation of packets.Summing signal amplifiers (not shown) may be used to combine signalsfrom sensing and driving electronics. By using a frequency filternetwork (not shown), electrode impedance sensing signals may be isolatedfrom the driving signals. For example, a constant current at sensingfrequency f_(s) may be applied to integrated electrode pairs to bemeasured. The sensing electronics 88, may then be operated at only theapplied frequency f_(s) to determine a voltage drops across theintegrated electrode pairs, thus allowing the impedance at the sensingfrequency f_(s) to be derived without interference from the drivingsignals.

[0094] In another embodiment, driving signals may be used to monitorelectrical impedance directly. Driving signals may be switched to one ormore integrated electrodes to generate a force to manipulate or interactpackets upon a reaction surface. Simultaneously, an electrical currentsensing circuit may be used to measure electrical current going throughthe energized integrated electrodes. Electrode impedances may be derivedfrom such measurements of electrical current.

[0095] Although any suitable device may be used, in one embodiment afunction generator is used as signal generator 82. More particularly, anarbitrary waveform signal generator in combination with voltage or poweramplifies or a transformer may be used to generate the requiredvoltages. In one embodiment, signal generator 82 may provide sine-wavesignals having a frequency up to the range of GHz and more particularlybetween about 1 kHz and about 10 MHz and a voltage between about 1 Vpeak-to-peak and about 1000 V peak-to-peak, and more particularly,between about 10 V peak-to-peak and about 100 V peak-to-peak.

[0096] As illustrated, signal generator 82 may be connected to anelectrode selector 84. Electrode selector 84 may apply one or moresignals from signal generator 82 to one or more individual electrodes(impedance sensing electrodes and/or driving electrodes may beindividually addressable). Electrode selector 84 may be one of a numberof suitable devices including a switch, a multiplexer, or the like.Alternatively, electrode selector 84 may apply one or more signals toone or more groups of electrodes. In one embodiment, selector 84 is madeof electronic switches or a multiplexer. Selector 84 may be digitallycontrolled. With the benefit of this disclosure, those of skill in theart will understand that selector 84 may be any suitable device that mayprogrammably divert one or more signals to one or more electrodes in anyarbitrary manner.

[0097] As illustrated in FIG. 6, controller 81 provides a feedback loopmechanism from impedance sensing electrodes 19 to driving electrodes 18via computer 80, which itself is coupled to signal generator 82,selector 84, and transducer 88. With the benefit of the presentdisclosure, those of skill in the art will recognize that controller 81may contain more or fewer components. The feedback mechanism allowscomputer 80 to tailor its commands to signal generator 82 according topositions of packets upon reaction surface 12, as determined byimpedance sensing electrodes 19. Thus, controller 81 allows for theadjustment of driving signals (and hence the adjustment of programmablemanipulation forces) according to positions of packets (as determined byimpedance sensing electrodes 19). In embodiments utilizing an integralarray of electrodes having integral impedance sensing electrodes 19 anddriving electrodes 18, a feedback mechanism may operate as follows.Positions of packets may be determined by measuring impedances betweenelectrical elements by applying impedance sensing signals to theintegral array. Position information may then be used to control drivingsignals to the integral array to perform microfluidic processing throughthe manipulation of packets. In one embodiment computer 80 may bereplaced by an application specific integrated circuit controller (ASIC)designed specifically for the purpose.

[0098]FIG. 7 shows an electrode driver 94 according to an embodiment ofthe presently disclosed method and apparatus. Driver 94 includes acomputer 80, a signal generator 82, a resistor network 100, a switchingnetwork 104, and a bitmap 108. Driver 94 is coupled to fluidic device 10which includes reaction surface 12 and an integral array 43.

[0099] Driver 94 may assist in the application of signals to integralarray 43 in order to direct microfluidic interactions of packets ofmaterial upon reaction surface 12. In one embodiment, computer 80directs signal generator 82 to apply an AC signal to integral array 43.In the illustrated embodiment, from signal generator 82 there may beprovided, for example, eight increasing voltage amplitudes usingresistor network 100, although more or fewer voltage amplitudes may beused. The eight AC signals may be distributed by switching network 104via connection 106 to the integral array 43 according to a bitmap 108 oraccording to any other suitable data structure stored in computer 80 orin another device. By modifying bitmap 108 via computer 80, differentvoltage amplitudes may be applied to different electrodes.

[0100] In one embodiment, signals to each electrode of integral array 43may be represented in bitmap 108 by 3 bits to address eight availablevoltage amplitudes. Voltage amplitude distributions of bitmap 108 may betransmitted sequentially to switching network 104 via connection 110twelve bits at a time using a communication protocol as is known in theart. In one embodiment, the communication protocol may use the followingconvention. To address a single electrode of integral array 43, thefirst four bits may specify the row of the array. The second four bitsmay specify the column of the array. The next three bits may specify thedesired voltage to be applied. The last bit may be used for errorcontrol by parity check. The rows/column arrangement may be used fordifferent layouts of arrays. For instance, the row/column convention ofaddressing may be used even for a hexagonal grid array configuration.Those skilled in the art will appreciate that other methods may be usedto address the electronic switching network 104 from computer 80.

[0101]FIG. 8 is side cross-section view of one embodiment of a fluidicdevice 10. Fluidic device 10 includes a wall 22 which encloses the sidesand top of a reaction surface 12 to form a reaction chamber 41. Reactionsurface 12 includes an integral array 43. Coupled to the integral arraymay be an interface board 54. Interface board 54 may interface theintegral array 43 with integrated circuits 50 via interconnect 55 andsolder bumps 52.

[0102] In the embodiment of FIG. 8, interface board 54 may be sandwichedbetween chamber 41 and integrated circuits 50. On one side, interfaceboard 54 may provide electrical signals (AC or DC) to electrodes ofintegral array 43, while the other side of interface board 54 mayinclude pads for flip-chip mounting of integrated circuits 50.Intermediate layers of interface board 54 may contain electrical leads,interconnects and vias, such as interconnect 55 to transfer power andsignals to and from electrodes of integral array 43 and integratedcircuits 50.

[0103] Interface board 54 may be fabricated using suitable PC-board andflip chip technologies as is known in the art. Suitable silk-screened orelectroplated flip-chip solder bump techniques may likewise be used.Alternatively, ink-jet solder deposition may be used as is known in theart.

[0104]FIG. 9 is a top view of an embodiment of a fluidic device 10. Inthe illustrated embodiment, fluidic device 10 is made up of fourdistinct 8 by 8 integral arrays 43, forming a 16 by 16 array. Under each8 by 8 array may be situated an integrated circuit (not shown in FIG. 9)that may provide control and signal processing to electrodes of theintegral array 43. The integral arrays may be coupled to a circuitconducting pad 34 that may be coupled to an interface conducting pad 36by a bond wire 38 (shown only in one quadrant). Connected to interfaceconducting pad 36 may be wire 42, or another suitable connector such asa PC board connector, leading to a computer or other suitablecontrolling device.

[0105]FIG. 9B is another top view of an embodiment of a fluidic device10. In this embodiment, many ports 15 are situated along edges offluidic device 10. These ports 15 may serve to inject and/or collectpackets 21 to/from reaction surface 12. Also illustrated is a sensor 122positioned adjacent a port 15. Such a sensor is described in referenceto FIG. 10 below.

[0106]FIG. 10 is a block diagram of a microfluidic processing system115. Processing system 115 may be designed to allow for control ofprogrammable dielectrophoretic array (PDA) 116 that serves as the sitefor microfluidic interactions and may be constructed in accordance withthe present disclosure. In view of its broad functionality, PDA 116 mayserve a role, in the field of fluidic processing, analogous to the roleplayed by a Central Processing Unit in the field of computers.

[0107] Coupled to PDA 116 are fluidic sensors 122. Fluidic sensors 122may measure and monitor fluid products from, in, or on PDA 116. Forinstance, fluidic sensors 122 may measure and identify reaction productsand may quantify reactions between packets. In one embodiment, fluidicsensors 122 may include an optical microscope or one or more sensors(chemical, electrochemical, electrical, optical, or the like), but anyother suitable monitoring device known in the art may be substitutedtherewith. For example, fluidic sensors 122 may be an electrochemicalsensor that monitors the presence and concentration of electroactive(redox-active) molecules in a packet solution. An electrochemical sensormay take the form of two or more microelectrodes. In a three-electrodeconfiguration, for example, electrodes may correspond to working,reference, and counter electrodes. A packet to be analyzed may be movedto be in contact with the three electrodes. A voltage signal may beapplied between the working and reference electrode, and the currentbetween the working and counter electrode may be monitored. Thevoltage-current relationship allows for the determination of thepresence or absence, and concentration of electro-active molecules inthe packet solution. Also attached to PDA 116 may be suitable materialinjection and extraction devices 120 coupled to appropriate inlet oroutlet ports of PDA 116 (not shown in FIG. 10). Such devices may be anysuitable structure allowing ingress to and egress from PDA 116.

[0108] In electrical communication with PDA 116 may be PDA voltagedrivers 126 and dielectric position sensors 124. PDA voltage drivers 126may be adapted to drive electrodes within PDA 116 so that an electricfield may be established that sets up manipulation forces thatmanipulate one or more packets of material within PDA 116 to promotemicrofluidic interactions. In one embodiment, PDA voltage drivers 126may include a signal generator and switching network as described inrelation to FIG. 7. Dielectric position sensors 124 may measurepositions of packets within PDA 116. In one embodiment, dielectricposition sensors 124 may include measuring devices connected toappropriate sensors that may determine a position of one or more packetsof material by sensing, for instance, a change in impedance betweenneighboring impedance sensing electrodes within PDA 116 and bycorrelating that change in impedance with a packet positioned adjacentthe neighboring sensors according to the teachings of the presentdisclosure.

[0109] Coupled to packet injection and extraction devices 120, PDAvoltage drivers 126, and dielectric position sensors 124 may be computerinterface 128. Computer interface 128 may be configured to allow hostcomputer 130 to interact with PDA 116. In one embodiment, computerinterface 128 may be a digital or analog card or board that may analyzeimpedance data to obtain a packet distribution map.

[0110] In the embodiment of FIG. 10, host computer 130 may be coupled tocomputer interface 128 to provide for control of PDA 116. Host computer130 may be coupled to position tracking agent 132 and to low-levelcontrol agent 134. Position tracking agent 132 may be adapted to store,process, and track positions of packets within the fluidic processor PDA116. Low-level control agent 134 may be configured to provideinstructions to host computer 130 from library interface 136 andsoftware interface 138. Library interface 136 may hold various sets ofsubroutines for programmably manipulating packets of materials on PDA116. Software interface 138 that may allow for custom programming ofinstructions to be executed by the fluidic processor PDA 116 toprogrammably manipulate packets. Alternatively established programs ofmanipulation instructions for specific fluid processing tests may beread from stored data and executed by the PDA fluid processor 116.

[0111]FIG. 11 illustrates operation of the presently disclosed methodand apparatus. In FIG. 11, open squares represent electrodes of anintegral array. However, it is contemplated that the description belowapplies equally well to a device utilizing separate impedance sensingelectrodes and driving electrodes.

[0112] In the illustrated embodiment, a packet 21 a may be introducedonto reaction surface 12 adjacent the location represented by integralimpedance sensor/electrode 201. The packet may be compartmentalized inan immiscible partitioning medium (not shown). The introduction of thepacket may be accomplished using an appropriate inlet port positionedadjacent to electrode 201. Alternatively, a packet may be introducedadjacent electrode 201 by applying an appropriate signal to electrode201 to generate an extraction force that may extract the packet from aninlet port or from an injector directly onto reaction surface 12 andadjacent to electrode 201.

[0113] Once positioned upon reaction surface 12, packet 21 a may be madeto move along a predetermined path indicated by dashed line 250. A pathmay be specified in a number of different ways. In one embodiment, auser may specifically define a path. For instance, one may specify apath, through appropriate programming of a controller or processingsystem, such as the one depicted numeral 250. Alternatively, a user mayspecify a starting position and an ending position to define a path. Forinstance, a user may specify that packet 21 a is to be introducedadjacent electrode 201 and end at a location adjacent electrode 215.Alternatively, one may specify a starting and ending location withspecific path information in between. For instance, a user may specify astarting position, an ending position, and a wavy path in between. Ascan be seen from FIG. 11, the path may have any arbitrary shape and itmay be programmed in any number of ways.

[0114] To move packet 21 a generally along the path, electrical signalsmay be suitably switched to integral impedance sensors/electrode pairsso that programmable manipulation forces may be created that act uponpacket 21 a to propel it generally along the specified path. Asdiscussed earlier, the signals may be varied in numerous ways to achievethe proper manipulation force. In the illustrated embodiment, applyingvoltage signals to electrode pairs 202 and 203 may create an attractivedielectrophoretic force that moves packet 21 a from electrode 201towards electrode 203 generally along path 250. As packet 21 a movesgenerally along a specified path, the integral array may measureimpedances to map the position of the packet upon reaction surface 12.Knowing the position of a packet allows manipulation forces to bedirected at appropriate positions to achieve a desired microfluidicprocessing task or interaction. In particular, knowing a position of apacket allows an appropriate signal to be switched to an appropriateelectrode or electrode pair to generate a manipulation force thatfurther propels or interacts the packet according to one or moreinstructions.

[0115] As packet 21 a moves from electrode 201 towards electrode 203,the impedance between electrode 202 and electrode 203 may change value,indicating that packet 21 a is between, or partially between, those twoelectrodes. The impedance may be measured as described in FIG. 3. Acontroller or processing system (not shown in FIG. 11) may register thelocation of packet 21 a and may apply a signal, for instance, toelectrode pairs 204 and 205, creating an attractive dielectrophoreticforce which propels packet 21 a towards those electrodes generally alongpath 250. As the impedance between electrode 204 and electrode 205changes value, a controller or processing system may apply a signal toelectrodes 206 and 207 to propel packet 21 a along path 250. As packet21 a continues along path 250, the impedance between electrode 206 andelectrode 207 may change value, indicating the presence of packet 21 aadjacent that location along the array. Thus, as packet 21 a moves alongpath 250, a controller or processing system may constantly monitor theposition of the packet by measuring impedance between electrode pairsand adjust electrical signals to an appropriate electrode or electrodepair (and hence, adjust manipulation forces) to continue to propel thepacket further along the specified path.

[0116] Measuring an impedance between pairs of electrodes not onlyallows a position of a packet to be determined, but it also allows forthe determination of a location of an obstruction or blockage uponreaction surface 12. For example, measuring the impedance betweenelectrodes 211 and 213 may indicate the presence of obstruction 212. Bynoting the position of obstruction 212, a controller or processingsystem may re-route one or more packets around the obstruction so thatno interference with microfluidic processing interactions occurs. Forexample, if a path is specified that passes through an area occupied byobstruction 212, a controller or processing system may modify electricalsignals to propel a packet generally along the specified path whileavoiding the obstruction. For instance, a stronger or weaker signal maybe sent to one or more electrodes or electrode pairs near obstruction212 to steer a packet clear of the blockage while still maintaining,generally, the path that was originally specified, and moreparticularly, the originally specified end point.

[0117] A controller or processing system according to the presentlydisclosed method and apparatus may be programmed to scan for severalobstructions and/or packets. Such a scan may build up a distributionmap, showing the location(s) of various packets and/or obstructions onan entire reaction surface 12 or a portion thereof. Such a distributionmap may be a virtual map, stored, for example, in a computer memory ordisplay. Turning again to FIG. 11, impedances of all electrode pairsadjacent to path 250 may be measured to determine if an obstructionblocks that path or if a packet lies somewhere in that area. If the pathis determined to be clear (e.g., if all the electrode pairs show animpedance value indicating a clear area), a packet may be safelypropelled generally along the path while avoiding any interactions withother packets and/or obstructions. However, if an obstruction isdiscovered, several different actions may be taken. In one embodiment,the user may be notified that a blockage exists along the specifiedpath. The user may then specify a different path or give anotherappropriate instruction. In another embodiment, the controller orprocessing system may determine if the obstruction may be avoided whilestill maintaining generally the same specified path. If possible,electrical signals may be modified and delivered to an electrode orelectrode pairs to generate appropriate electrical field distributionsthat set up proper manipulation forces that will aid in avoiding theobstruction. Because, at least in part, of this ability to constantlymeasure positions and responses of packets during manipulation, acontroller or processing system may be capable of monitoring theintegrity of fluidic processing, reporting and correcting any errorsthat may occur.

[0118]FIG. 11 also depicts how processing may be carried out on twopackets. In the illustrated embodiment, a second packet 21 b begins onreaction surface 12 near electrode 217. A second path, path 260, may bespecified that ends at electrode 219. As can be seen, paths 250 and 260may cross at interaction point 240. At interaction point 240, the twopackets may interact in many ways as illustrated, for example, in FIG.12. The interaction may include, but is not limited to, fusing, merging,mixing, reacting, dividing, splitting, or any combination thereof. Forinstance, the two packets may interact at interaction point 240 to formone or more intermediate or final reaction products. Those products maybe manipulated in the same or in a similar manner as the two originalpackets were manipulated.

[0119]FIG. 11 also depicts how maintenance may be performed uponreaction surface 12. A maintenance packet 21 c adapted to performmaintenance upon reaction surface 12 may be introduced onto reactionsurface 12 by a maintenance port (not shown in FIG. 11). A maintenanceport may be similar to an inlet port in structure but may be dedicatedto the introduction of one or more maintenance packets 21 c designedspecifically, for instance, to clean or maintain reaction surface 12, asurface coating, or one or more electrodes or sensors. Maintenancepacket 21 c may also react with an obstruction in such a way as toremove that obstruction. As illustrated, maintenance packet 21 c maybegin near electrode 241. It may then be propelled along path 270,providing maintenance, perhaps, to electrodes 242 and 243. Maintenancepacket 21 c may be propelled back to a maintenance port, extracted fromreaction surface 12, and later used again, or it may discarded at anoutlet part.

[0120]FIG. 12 demonstrates several different possible fluidicinteractions that may be carried out using the presently disclosedmethod and apparatus. In the illustrated embodiment, packets 21 (onlyone is labeled for convenience) reside upon a reaction surface 12 havingan integral array 43 (only one electrode is labeled for convenience). Inthe top pane of FIG. 12, there is shown an interaction in which a singlepacket is manipulated on the reaction surface by moving the packet in aprogrammed fashion. In the middle pane, two packets, starting atdifferent locations upon the reaction surface, are directed, viaappropriate electrical signals, to come together at a specified location(near the center of the array) to fuse together, for example, toinitiate a reaction. The fused packet may be manipulated just as theoriginal packets were manipulated. For instance, the fused packet may bemoved to various locations or it may fuse again with another packet(s).Shown in the bottom pane of FIG. 12 is a splitting interaction. Asshown, a single packet is subjected to different programmablemanipulation forces that cause the packet to split into two distinctpackets. Such an interaction may be accomplished by, first, noting theposition of the packet to be split, and then by applying appropriatesignals to electrode pairs to generate two or more opposing forces thatcause the packet to split apart.

[0121]FIG. 13 is a flowchart showing one embodiment of a method ofoperation. A material may be introduced onto a reaction surface andcompartmentalized to form one or more packets in step 300. Multiplematerials may be introduced at different locations along reactionsurface 12 to form a plurality of packets. A path may be specified as instep 310. The path may be designed to accomplish any type ofmicrofluidic processing, manipulation, or interaction. Differentreactions may be performed in serial or in parallel according todifferent paths. Instructions governing such processing may be embodiedin the pseudo-code that may be routed through computer interface 128 ofFIG. 10. Illustrative code may read as follows:

EXAMPLE Avidin Actin.PSL

[0122] Use inlet(1-3), outlet(1-2) Inlet(1) is actin Inlet(2) is avidinInlet(3) is enzyme Outlet(1) is polymer Outlet(2) is waste Matrix(1,2)is accumulator Clean Do Sactin = (Pull actin) // pull a new packet onthe next Savidin = (Pull avidin) // available matrix element next toSenzyme = (Pull enzyme) // the inlets Move Sactin into accumulator //merges components and enzyme Move Savidin into accumulator // in asingle packet Move Senzyme into accumulator Wait 1000ms ShiftRowaccumulator.row,+1 // drag packet left into polymer outlet Move0.5*accumulator into // drag half packet to row 2 (2,accumulator.column)ShiftRow 2, +1 // drag packet left into waste Loop Until polymer.count =10 // number of packet at polymer outlet = 10 Clean

[0123] In step 315, computer 80 of FIG. 6 or any other suitable devicemay determine the next unit step along the path specified in step 315.In other words, a path may be broken down into unit steps and the nextunit step or steps may be determined with respect to the specified path.In step 320, a programmable manipulation force is generated on reactionsurface 12 through the use of any of the mechanisms disclosed herein.The programmable manipulation force may manipulate the one or morepackets according to instructions from a user. In step 330, theresponse(s) of the one or more packets may be monitored. This step mayinclude measuring an impedance on the reaction surface as discussedherein. In particular, one may determine whether the one or more packetsmoved to where they were supposed to, or whether they interacted asinstructed. In step 340, it may be determined if the packet movement wassuccessful —that is, it may be determined whether the packet ended up ata location corresponding to the unit step determined in step 315.

[0124] If a packet movement was successful (i.e., if the packetresponded correctly to the programmable manipulation force(s)), then itmay be determined, by comparison with the specified path, whether or notthe packet destination has been reached. In other words, it may bedetermined if the packet has moved to the end location of the specifiedpath. If the destination has not been reached, the next unit stepmovement may be determined at step 315 and steps 320, 330, 340, and 365may be repeated. If the destination has been reached, it may bedetermined whether another packet is to be manipulated in step 370. Thisstep may include a user prompt. If no further packets are to bemanipulated, it may be determined whether fluidic processing is completein step 380. If yes, the process may be ended at step 390. Step 390 mayinclude the collecting of one or more packets, further analysis,throwing away of the reaction surface, or any procedure describedherein. If the processing is not complete, the next step of processingmay be determined in step 395. The next step may entail, for example,the introduction of another packet, the specification of another path,or any other step of FIG. 13.

[0125] If a packet manipulation is unsuccessful (i.e., if the appliedprogrammable manipulation force(s) did not produce a desired interactionor movement along a specified path as indicated by step 340), one maylocate an obstruction upon the reaction surface as indicated in step 350and as taught herein. After locating any obstructions, a new, modifiedpath may be determined or specified as indicated by step 360, leading tostep 310.

[0126] As mentioned with relation to FIG. 1, the present disclosurecontemplates that many different types of forces may be utilized as amanipulation force for promoting fluidic interactions among packets ofmaterial on a reaction surface. Specifically, suitable forces other thandielectrophoresis include electrophoretic forces, optical forces,mechanical forces, or any combination thereof. Below are discussedembodiments of the present disclosure dealing with electrophoretic andoptical manipulation forces.

[0127] Programmable Electrophoretic Array (PEA)

[0128] A fluidic processing system incorporating a programmableelectrophoretic array may be constructed according to the presentdisclosure. As used herein, “programmable electrophoretic array” (PEA)refers to an electrode array whose individual elements can be addressedwith DC, pulsed, or low frequency AC electrical signals (typically, lessthan about 10 kHz) electrical signals. The addressing of electrodeelements with electrical signals initiates different field distributionsand generates electrophoretic manipulation forces that trap, repel,transport or perform other manipulations upon charged packets on andabove the electrode plane. By programmably addressing electrode elementswithin the array with electrical signals, electric field distributionsand electrophoretic manipulation forces acting upon charged packets maybe programmable so that packets may be manipulated along arbitrarilychosen or predetermined paths. A PEA may utilize electrophoretic forcesin DC or low-frequency (typically, less than about 10 kHz) AC electricalfields. Such electrophoretic forces may be used instead of, or inaddition to, another manipulation forces such as dielectrophoresis.

[0129] Negative or positive charges may be induced or injected intofluid packets. The charged packets may be moved or manipulated byelectrophoretic forces generated by an electrode array fabricated on aninner surfaces of a chamber in accordance with this disclosure. Theelectrode array, termed a programmable electrophoretic array (PEA), mayconsist of uniformly or non-uniformly spaced electrode elements.Individual electrode elements may be independently addressable with DC,pulsed, or low frequency AC electrical signals (<about 10 kHz).Characteristic dimensions of individual electrode elements may be of anysize but, in one embodiment, may lie between 0.2 micron and 10 mm.Individual electrode elements may take similar or different geometricalforms such as squares, circles, diamonds, or other shapes. Programmablyswitchable electrical signals may be applied to individual electrodeelements so that a programmable electrical field distribution may begenerated. Such a distribution may impose electrophoretic forces totrap, repel, transport or manipulate charged packets in a partitioningmedium. Further, electrical signals may be applied to such an array sothat a packet may be broken down to two or more packets. Theprogrammability of a PEA may be reflected in the fact that the electricfield distributions and electrophoretic forces acting on charged packetsmay be programmable so that charged packets may be trapped or repelledor transported along arbitrarily chosen paths in the partitioningmedium, and that a PEA may be programmed to perform different reactionsin series or in parallel where different manipulation protocols ofpackets (differing in size, number, and/or reagent type concentration)may be required. As with PDA surface modification, if a dielectric layercoating is applied to the surface of a PEA to modify interaction forcesbetween packets reaction surfaces, the dielectric layer may be madesufficiently thin (typically 2 nm to 1 micron) to allow for electricfield penetration.

[0130] Optical Manipulation

[0131] Optical tweezers (which may consist of a focused laser beam witha light intensity gradient) may be also be used for trapping andmanipulating packets of material. Optical manipulation requires that therefractive indices of the packets be different from that of theirsuspending medium, for instance, a partitioning medium as describedherein. As light passes through one or more packets, it may inducefluctuating dipoles. Those dipoles may interact with electromagneticfield gradients, resulting in optical forces directed towards or awayfrom the brighter region of the light. If their refractive indices arehigher than that of the partitioning medium, packets may be trapped in abright region, and when the laser light moves with respect to thepartitioning medium, packets may follow the light beam, allowing foroptical manipulation forces. Conversely, if the packets have refractiveindices smaller than their partitioning medium, they will experienceforces directing them away from bright regions.

[0132] Therefore, if packets have different refractive indexes from thatof the partitioning medium (e.g., water packets in air or oil), opticaltweezers may exert forces on them. Therefore, to manipulate and interactpackets, a microscope or other optical system incorporating one or morelaser tweezers may be used. A chamber containing a partitioning mediumin accordance with the present disclosure may be placed into such anoptical system. Following the introduction of packets of material intothe chamber, laser tweezers may be used to trap packets. By moving thefocal point of the optical tweezers with respect to the partitioningmedium (e.g., moving a stage holding the thin chamber containing thepartitioning medium whilst fixing the position of laser tweezers and/orby focusing the laser beam to different depths in the partitioningmedium), packets may be manipulated as described herein. Through the useof apparatus such as a computer-controllable, multi-axis translationstage, the movement of the optical tweezers with respect to thesuspending medium may be programmed or automatically controlled. Thusthe optical tweezer may be moved, with respect to the medium, along anyarbitrarily chosen or predetermined paths. By doing so, packets underthe influences of the optical tweezers may be manipulated along anyarbitrarily chosen or predetermined paths.

Example 1

[0133] Aqueous materials have been compartmentalized to form packetsusing hydrophobic liquids as a partitioning medium. Partitioning mediumsso used have included decane, bromodocane, mineral oil, and 3 in 1™ oil.Packets have been formed by briefly sonicating about 3 milliliters ofthe hydrophobic liquid to which had been added 20 to 50 microliters ofaqueous medium. Aqueous media tested have included deionized water, tapwater (electrical conductivity of about 40 mS/m) and phosphate bufferedsaline (PBS) solution.

Example 2

[0134] Aqueous packets suspended in mineral oil, bromodoecane and 3 in1™ oil have been collected by dielectrophoresis by applying sinusoidalsignals to gold-on-glass electrode arrays having 20, 80 and 160 micronspacing, respectively. The 20-micron electrode array consisted ofparallel line electrodes (20 microns in width and spacing). The 80 and160 micron electrode arrays were of the interdigitated, castellatedgeometries. Aqueous packets were collected at electrode edges or tipswhen AC voltage signals between 100 Hz and 20 MHz were applied. Appliedvoltages were from 10 to 100 V peak-to-peak. The formation ofpearl-chains of water packets has also been observed.

Example 3

[0135] Aqueous packets in hydrophobic suspension have been broughttogether and fused under the influence of dielectrophoretic forces onthe same electrode arrays used in Example 2.

Example 4

[0136] Packets have been moved from one electrode element to anotherunder influence of dielectrophoretic forces when the AC electrical fieldis switched on an addressable array of parallel line electrodes having20 micron width and spacing.

Example 5

[0137] Sensitive AC impedance monitors have been built for use withmicroelectrode arrays. Such monitors may provide for sensitivedielectric sensing of packet positions.

[0138] While the present disclosure may be adaptable to variousmodifications and alternative forms, specific embodiments have beenshown by way of example and described herein. However, it should beunderstood that the present disclosure is not intended to be limited tothe particular forms disclosed. Rather, it is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the disclosure as defined by the appended claims. Moreover,the different aspects of the disclosed apparatus and methods may beutilized in various combinations and/or independently. Thus theinvention is not limited to only those combinations shown herein, butrather may include other combinations.

What is claimed is:
 1. An apparatus for programmably manipulating a packet, said apparatus comprising: a reaction surface configured to provide an interaction site for said packet; an inlet port coupled to said reaction surface and configured to introduce said packet onto said reaction surface; means for generating a programmable manipulation force upon said packet to programmably move said packet about said reaction surface along arbitrarily chosen paths; and a position sensor coupled to said reaction surface and configured to sense a position of said packet on said reaction surface; and a controller coupled to said means for generating a programmable manipulating force and to said position sensor, said controller configured to adjust said programmable manipulation force according to said position.
 2. The apparatus of claim 1, further comprising an outlet port coupled to said reaction surface and configured to collect said packet from said reaction surface.
 3. The apparatus of claim 1, wherein said means for generating a manipulation force comprises a conductor adapted to generate an electric field.
 4. The apparatus of claim 1, wherein said means for generating a manipulation force comprises a light source.
 5. The apparatus of claim 1, wherein said manipulation force comprises a dielectrophoretic force, an electrophoretic force, an optical force, a mechanical force, or any combination thereof.
 6. The apparatus of claim 1, wherein said position sensor comprises a conductor configured to measure an electrical impedance of said packet.
 7. The apparatus of claim 1, wherein said position sensor comprises an optical system configured to monitor said position of said packet.
 8. The apparatus of claim 1, wherein said means for generating a programmable manipulation force and said position sensor are integral.
 9. An apparatus for microfluidic processing by programmably manipulating packets, said apparatus comprising: a reaction surface configured to provide an interaction site for said packets; an inlet port coupled to said reaction surface and configured to introduce said packets onto said reaction surface; an array of driving electrodes coupled to said reaction surface and configured to generate a programmable manipulation force upon said packets to direct said microfluidic processing by moving said packets along arbitrarily chosen paths; and an array of impedance sensing electrodes coupled to said reaction surface and configured to sense a position of said packets during said microfluidic processing.
 10. The apparatus of claim 9, further comprising an outlet port coupled to said reaction surface and configured to collect said packets from said reaction surface.
 11. The apparatus of claim 9, further comprising a controller coupled to said array of driving electrodes and to said array of impedance sensing electrodes, said controller adapted to provide a feedback from said array of impedance sensing electrodes to said array of driving electrodes.
 12. The apparatus of claim 9, wherein said array of driving electrodes and said array of impedance sensing electrodes are integral.
 13. The apparatus of claim 9 further comprising an integrated circuit coupled to said array of driving electrodes and to said array of impedance sensing electrodes.
 14. The apparatus of claim 9 further comprising a coating modifying a hydrophobicity of said reaction surface.
 15. The apparatus of claim 9, further comprising a maintenance port.
 16. An apparatus for processing packets in a partitioning medium, said apparatus comprising: a chamber configured to contain said packets and said partitioning medium; a programmable dielectrophoretic array coupled to said chamber and configured to generate a programmable dielectrophoretic force to direct processing of said packets; and an impedance sensing array of electrodes integral with said programmable dielectrophoretic array, said impedance sensing array of electrodes configured to sense a position of said packets within said chamber.
 17. The apparatus of claim 16, further comprising an integrated circuit coupled to said programmable dielectrophoretic array and to said impedance sensing array of electrodes.
 18. The apparatus of claim 16, further comprising a controller coupled to said programmable dielectrophoretic array and to said impedance sensing array of electrodes, said controller adapted to provide a feedback from said impedance sensing array of electrodes to said programmable dielectrophoretic array.
 19. The apparatus of claim 16, wherein said electrodes are between about 1 micron and about 200 microns and are spaced between about 1 micron and about 200 microns.
 20. A method for manipulating a packet, comprising: providing a reaction surface, an inlet port coupled to said reaction surface, means for generating a programmable manipulation force upon said packet, a position sensor coupled to said reaction surface, and a controller coupled to said means for generating a programmable manipulation force and to said position sensor; introducing a material onto said reaction surface with said inlet port; compartmentalizing said material to form said packet; sensing a position of said packet with said position sensor; applying a programmable manipulation force on said packet at said position with said means for generating a programmable manipulation force, said programmable manipulation force being adjustable according to said position by said controller; programmably moving said packet according to said programmable manipulation force along arbitrarily chosen paths.
 21. The method of claim 20, wherein said packet comprises a fluid packet, an encapsulated packet, or a solid packet.
 22. The method of claim 20, wherein said compartmentalizing comprises suspending said material in a partitioning medium.
 23. The method of claim 22, wherein said material is immiscible in said partitioning medium.
 24. The method of claim 22, wherein said reaction surface includes a coating, and a hydrophobicity of said coating is greater than a hydrophobicity of said partitioning medium.
 25. The method of claim 20, wherein said applying a programmable manipulation force comprises applying a driving signal to one or more driving electrodes arranged in an array to generate said programmable manipulation force.
 26. The method of claim 20, wherein said programmable manipulation force comprises a dielectrophoretic force, an electrophoretic force, an optical force, a mechanical force, or any combination thereof.
 27. The method of claim 20, wherein said sensing a position comprises applying a sensing signal to one or more impedance sensing electrodes arranged in an array to detect an impedance associated with said packet.
 28. The method of claim 20, further comprising interacting said packet, wherein said interacting comprises moving, fusing, merging, mixing, reacting, metering, dividing, splitting, sensing, collecting, or any combination thereof.
 29. A method of fluidic processing, said method comprising: providing a reaction surface, an inlet port coupled to said reaction surface, an array of driving electrodes coupled to said reaction surface, and an array of impedance sensing electrodes coupled to said reaction surface; introducing one or more materials onto said reaction surface with said inlet port; compartmentalizing said one or more materials to form a plurality of packets; applying a sensing signal to one or more of said impedance sensing electrodes to determine a position of one or more of said plurality of packets; and applying a driving signal to one or more of said driving electrodes to generate a programmable manipulation force on one or more of said plurality of packets at said position; and interacting one or more of said plurality of packets according to said programmable manipulation force.
 30. The method of claim 29, wherein at least one of said plurality of packets comprises a fluid packet, an encapsulated packet, or a solid packet.
 31. The method of claim 29, wherein said sensing signal and said driving signal comprise a single processing signal.
 32. The method of claim 31, wherein said processing signal comprises a first frequency component corresponding to said sensing signal and a second frequency component corresponding to said driving signal.
 33. The method of claim 29, further comprising forming a packet distribution map according to said positions of said plurality of packets.
 34. The method of claim 29, further comprising determining a position of one or more obstructions on said reaction surface.
 35. The method of claim 29, wherein said interacting comprises moving, fusing, merging, mixing, reacting, metering, dividing, splitting, sensing, collecting, or any combination thereof.
 36. A method for manipulating one or more packets on a reaction surface, comprising: providing a programmable dielectrophoretic array coupled to said reaction surface and an impedance sensing array of electrodes integral with said programmable dielectrophoretic array; introducing a material onto said reaction surface; compartmentalizing said material to form said one or more packets; specifying a path upon said reaction surface; applying a programmable manipulation force with said programmable dielectrophoretic array on said one or more packets to move said one or more packets along said path; sensing a position of said one or more packets with said impedance sensing array of electrodes; monitoring whether said position corresponds to said path; and interacting said one or more packets.
 37. The method of claim 36, wherein at lease one of said one or more packets comprises a fluid packet, an encapsulated packet, or a solid packet.
 38. The method of claim 36, further comprising: sensing a position of an obstruction; determining a modified path, said modified path avoiding said obstruction; and applying a programmable manipulation force on said one or more packets to move said one or more packets along said modified path.
 39. The method of claim 36, wherein said specifying a path comprises specifying an initial position and a final position.
 40. The method of claim 36, wherein said introducing a material comprises extracting said material with a dielectrophoretic extraction force from an injector onto said reaction surface.
 41. The method of claim 36, wherein said interacting comprises moving, fusing, merging, mixing, reacting, metering, dividing, splitting, sensing, collecting, or any combination thereof. 